﻿#region Copyright & License

//
// Author: Ian Davis <ian.f.davis@gmail.com> Copyright (c) 2007-2008, Ian Davs
//
// Portions of this software were developed for NUnit. See NOTICE.txt for more
// information. 
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
//

#endregion

#region Using Directives

using System;

#endregion

namespace Ensurance.Constraints.Comparison
{
    /// <summary>
    /// Abstract base class for constraints that compare values to determine if
    /// one is greater than, equal to or less than the other.
    /// </summary>
    public class ComparisonConstraint<T> : Constraint<T>
    {
        /// <summary>
        /// The predicate used as a part of the description
        /// </summary>
        private string Predicate { get; set; }

        /// <summary>
        /// Initializes a new instance of the <see cref="ComparisonConstraint{T}"/>
        /// class.
        /// </summary>
        /// <param name="value">The value against which to make a comparison.</param>
        /// <param name="ltOK">if set to <c>true</c> less succeeds.</param>
        /// <param name="eqOK">if set to <c>true</c> equal succeeds.</param>
        /// <param name="gtOK">if set to <c>true</c> greater succeeds.</param>
        /// <param name="predicate">String used in describing the constraint.</param>
        protected ComparisonConstraint( IComparable value, bool ltOK, bool eqOK, bool gtOK, string predicate )
        {
            Expected = value;
            LessThanReturnsOK = ltOK;
            EqualReturnsOK = eqOK;
            GreaterThanReturnsOK = gtOK;
            Predicate = predicate;
        }

        /// <summary>
        /// if true, equal returns success
        /// </summary>
        protected internal bool EqualReturnsOK { get; set; }

        /// <summary>
        /// The value against which a comparison is to be made
        /// </summary>
        protected internal IComparable Expected { get; set; }

        /// <summary>
        /// if true, greater than returns success
        /// </summary>
        protected internal bool GreaterThanReturnsOK { get; set; }

        /// <summary>
        /// If true, less than returns success
        /// </summary>
        protected internal bool LessThanReturnsOK { get; set; }

        /// <summary>
        /// Test whether the constraint is satisfied by a given value
        /// </summary>
        /// <param name="actual">The value to be tested</param>
        /// <returns>True for success, false for failure</returns>
        public override bool IsSatisfiedBy( T actual )
        {
            Actual = actual;
            int icomp = Numerics.Compare( Expected, actual );
            return icomp < 0 && GreaterThanReturnsOK || icomp == 0 && EqualReturnsOK || icomp > 0 && LessThanReturnsOK;
        }

        /// <summary>
        /// Write the constraint description to a MessageWriter
        /// </summary>
        /// <param name="writer">The writer on which the description is displayed</param>
        /// <exception cref="ArgumentNullException">if the message writer is null.</exception>
        public override void WriteDescriptionTo( IMessageWriter writer )
        {
            if ( writer == null )
            {
                throw new ArgumentNullException( "writer" );
            }
            writer.WritePredicate( Predicate );
            writer.WriteExpectedValue( Expected );
        }
    }
}